fix: support bracket index in @cast expressions, to enable type narrowing for array element access

crates/emmylua_code_analysis/src/diagnostic/test/param_type_check_test.rs

@@ -1555,4 +1555,36 @@ mod test {
         "#,
         ));
     }
+
+    #[test]
+    fn test_cast_bracket_index_narrows_type() {
+        let mut ws = VirtualWorkspace::new();
+
+        // @cast addresses[1] -nil should narrow addresses[1] from string|nil to string
+        assert!(ws.check_code_for(
+            DiagnosticCode::ParamTypeMismatch,
+            r#"
+            ---@param addr string
+            local function connect(addr) end
+
+            ---@type string[]
+            local addresses = { "127.0.0.1" }
+            ---@cast addresses[1] -nil
+            connect(addresses[1])
+        "#,
+        ));
+
+        // Without @cast, addresses[1] is string|nil, should report param-type-mismatch
+        assert!(!ws.check_code_for(
+            DiagnosticCode::ParamTypeMismatch,
+            r#"
+            ---@param addr string
+            local function connect(addr) end
+
+            ---@type string[]
+            local addresses = { "127.0.0.1" }
+            connect(addresses[1])
+        "#,
+        ));
+    }
 }

crates/emmylua_code_analysis/src/diagnostic/test/undefined_field_test.rs

@@ -818,4 +818,45 @@ mod test {
         "#
         ));
     }
+
+    #[test]
+    fn test_intersection_array_index_access() {
+        let mut ws = VirtualWorkspace::new();
+
+        // Explicit intersection type annotation
+        assert!(ws.check_code_for(
+            DiagnosticCode::UndefinedField,
+            r#"
+            ---@type integer[] & { n: integer }
+            local values
+            local e = values[1]
+            "#
+        ));
+    }
+
+    #[test]
+    fn test_array_index_with_cast() {
+        let mut ws = VirtualWorkspace::new();
+
+        // Accessing [1] on a string[] should not report undefined-field
+        assert!(ws.check_code_for(
+            DiagnosticCode::UndefinedField,
+            r#"
+            ---@type string[]
+            local addresses
+            local a = addresses[1]
+            "#
+        ));
+
+        // Accessing [1] on a string[] with @cast should not report undefined-field
+        assert!(ws.check_code_for(
+            DiagnosticCode::UndefinedField,
+            r#"
+            ---@type string[]
+            local addresses
+            ---@cast addresses[1] -nil
+            local a = addresses[1]
+            "#
+        ));
+    }
 }

crates/emmylua_parser/src/grammar/doc/tag.rs

@@ -499,16 +499,41 @@ fn parse_cast_expr(p: &mut LuaDocParser) -> DocParseResult {
     let m = p.mark(LuaSyntaxKind::NameExpr);
     p.bump();
     let mut cm = m.complete(p);
-    // 处理多级字段访问
-    while p.current_token() == LuaTokenKind::TkDot {
-        let index_m = cm.precede(p, LuaSyntaxKind::IndexExpr);
-        p.bump();
-        if p.current_token() == LuaTokenKind::TkName {
-            p.bump();
-        } else {
-            // 找不到也不报错
+    // 处理多级字段访问（支持 `.` 和 `[]` 索引）
+    loop {
+        match p.current_token() {
+            LuaTokenKind::TkDot => {
+                let index_m = cm.precede(p, LuaSyntaxKind::IndexExpr);
+                p.bump();
+                if p.current_token() == LuaTokenKind::TkName {
+                    p.bump();
+                }
+                cm = index_m.complete(p);
+            }
+            LuaTokenKind::TkLeftBracket => {
+                let index_m = cm.precede(p, LuaSyntaxKind::IndexExpr);
+                p.bump();
+                // Wrap the index value in a LiteralExpr node so that
+                // LuaIndexExpr::get_index_key() can find it (it expects
+                // a child Node, not a bare token).
+                if p.current_token() == LuaTokenKind::TkInt
+                    || p.current_token() == LuaTokenKind::TkString
+                {
+                    let literal_m = p.mark(LuaSyntaxKind::LiteralExpr);
+                    p.bump();
+                    literal_m.complete(p);
+                } else if p.current_token() == LuaTokenKind::TkName {
+                    let name_m = p.mark(LuaSyntaxKind::NameExpr);
+                    p.bump();
+                    name_m.complete(p);
+                }
+                if p.current_token() == LuaTokenKind::TkRightBracket {
+                    p.bump();
+                }
+                cm = index_m.complete(p);
+            }
+            _ => break,
         }
-        cm = index_m.complete(p);
     }
 
     Ok(cm)

crates/emmylua_parser/src/lexer/lua_doc_lexer.rs

@@ -599,11 +599,24 @@ impl LuaDocLexer<'_> {
                 reader.bump();
                 LuaTokenKind::TkDot
             }
+            '[' => {
+                reader.bump();
+                LuaTokenKind::TkLeftBracket
+            }
+            ']' => {
+                reader.bump();
+                LuaTokenKind::TkRightBracket
+            }
             ch if is_name_start(ch) => {
                 reader.bump();
                 reader.eat_while(is_name_continue);
                 LuaTokenKind::TkName
             }
+            ch if ch.is_ascii_digit() => {
+                reader.bump();
+                reader.eat_while(|c| c.is_ascii_digit());
+                LuaTokenKind::TkInt
+            }
             _ => self.lex_normal(),
         }
     }